It's a concept that's all the rage on many college campuses nowadays. It can be applied to many facets, so if you're a American-born, white, male, heterosexual, temporarily-able bodied, and aged 21-60... then our society practically worships you and heaps upon you all sorts of undeserved/unearned things solely on the basis of such physical attributes. "Check your privilege" is a phrased used to call out someone that is not seen as being sensitive enough to the systemic "unfairness" that others, outside their given privileged status, have to suffer with in life.